1. Field of the Invention
The present invention relates to an evaporator, a heat absorber and a thermal transport system.
2. Description of the Related Art
Thermal transport systems such as CPL (Capillary Pumped Loop) and LHP (Looped Heat Pipe) are commonly used in various applications like spacecraft, industrial machinery and home apparatus.
Since an evaporator of these thermal transport systems has a very narrow and thin structure therefore multi-connection of the evaporators is required to cover a wide range of heat generation area or distributed heat generation areas.
In this respect, previously, a parallel connection of CPL evaporators is adopted as shown in FIG. 11.
However, the parallel connection has disadvantages that: 1) liquid-phase working fluid in each evaporator dries out quickly, because it is difficult to equalize a liquid supply to each evaporator; and 2) pressure control within a loop is difficult.
Therefore, a conventional system is supported by an external pump for equalizing the liquid supply and an extra liquid reservoir tank attaching a heater for adjusting liquid pressure. However such additional components caused complicated, large and heavyweight configuration and high manufacturing cost.
Description of the numbered components follows: an evaporator 1 for receiving heat generated at a heat generation unit (not illustrated), a vapor line 5 where working fluid vaporized at the evaporator 1 (hereafter also called “vapor”) flows, a condenser 7 for rejecting the heat, a liquid supply line 8 where working fluid condensed at the condenser 7 (hereunder also called “liquid”) flows, an arrow 20 showing a direction of vapor flow in the vapor line 5, an arrow 21 showing a direction of liquid flow, a board 26 incorporating the heat generation unit, an extra liquid reservoir 41, a heater 42, a by-pass valve 43, and a pump 44,
Within a loop formed by the vapor line 5, the condenser 7, and the liquid supply line 8, an uncolored portion shows the vapor flows, and a black portion shows the liquid flows.
Next a function of the conventional thermal transport system is explained.
The evaporator 1 installs the porous structured wick at its inner wall. Liquid-phase working fluid in the evaporator 1 penetrates the wick by the effect of a capillary force of the wick.
The heat from the heat generation unit vaporizes the liquid penetrating the wick, and the vapor moves from the evaporator 1 to the vapor line 5. Soon, the vapor is cooled down and condensed at the condenser 7. The liquid condensed at the condenser 7 returns to the evaporator 1 via the liquid supply line 8 and the by-pass valve 43.
The liquid returns to the evaporator 1 by the action of the capillary force of the wick, however the capillary force of the wick is limited. When an amount of heat generated in the system increases, or in other words, when a heating value becomes high, the capillary force of the wick by itself cannot return the liquid to the evaporator 1. Consequently, the liquid supply to each liquid reservoir in the evaporator 1 stops and the liquid reservoir 1 dries out.
In order to prevent this problem, the conventional system adopts an external pump 44 so as to assist the capillary force of the wick.
In this case, the by-pass valve 43 is closed in order for the liquid to flow into the channel where the pump is. But a certain amount of the liquid goes to the by-pass valve 43 and remains stagnant about the by-pass valve 43, therefore a distribution of the liquid in the system changes.
In addition, the conventional system uses the extra liquid reservoir 41 attaching the heater 42 so as to secure adequate liquid supply to each evaporator 1.
The heater 42 raises the temperature in the extra liquid reservoir 41 to raise a pressure in the extra liquid reservoir 41. This raised pressure allows the liquid in the extra liquid reservoir to flow out.
As mentioned above, as the parallel connection of the evaporators 1 needs the pump and other devices, the configuration of the system has to be complicated and large.
The reason why the pumps and other components are required is that the capillary force of the wick itself is insufficient.
FLHP (Flexible Looped Heat Pipe) has a higher maximum heat transport capability and a longer transport distance than the conventional heat devices of CPL or a rigid heat pipe, therefore FLHP is expected to be a promising heat transport device for space satellites, electronics and so on.
As an evaporator 1 of FLHP also has a narrow shape like other heat transport devices, multi-connection of the FLHP evaporators 1 is required in cases of covering a wide range of heat generating area or distributed heat generation areas.
But the multi-connection of FLHP evaporators 1 had never been demonstrated.
Hence, multi-connection technique applied to FLHP has been desired.
As explained, the parallel connection of the evaporators has the disadvantages of the configuration being complex, large, heavyweight and expensive.
Therefore, the present invention aims to resolve such disadvantages and to introduce an evaporator, a heat absorber and a thermal transport system of simple, small, lightweight and cost effective structure.